Electric switch head



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United States Patent "ice 3,259,723 ,ELECTRIC SWITCH HEAD Russell S. Davis, Detroit, Mich., assignor to I-T-E Circuit Breaker Company, Philadelphia, Pa., a corporation of Pennsylvania Filed Oct. 4, 1963, Ser. No. 313,939 2 Claims. (Cl. 200144) This invention relates to improvements in molded switch heads of the type illustrated in US. Patent 2,820,123 with the improvements being such that the switching device is capable of closing on a faulted high current electrical circuit without destroying the switch head or rendering the switch inoperative.

Switches of the type under consideration provide first and second spaced stationary contacts which are engaged and disengaged by a movable contact slug passing between the contacts and carried by a molded housing guided for rectilinear movement by the stationary contacts. The switch head also includes an insulating barrier which moves between the stationary contacts as the contact slug is moved to disengaged position with the barrier serving to decrease arcing between the stationary contacts and the movable contacts. Arcing is further reduced since the quantity of gas present is restricted by the close fit between the housing of the switch head and the stationary contacts.

In switch heads of the type under consideration, prior art constructions have been such that upon closing on a very high current circuit with a fault the contact slug engages the stationary contacts allowing current to start flowing through the slug from one stationary contact to the, other. For the most part prior art switch heads are provided with steel clamping springs which are constructed so that they do not engage the stationary contacts until a substantial period of time after engagement of the stationary contacts by the slug. Because of this extended time interval, even before engagement of the stationary contact by the clamping spring switch current rises to a very high magnitude with the high current producing a magnetic force acting between stationary contacts tending to force them apart. Thus, the stationary contacts break contact with the slug so that an arc strikes from the stationary contacts to the clamping spring because of the poor contact at the slug.

It has been found that this arcing burns or disintegrates the clamping spring so as to. render it useless during subsequent switch operations. Further, intense heat is generated inthe contact slug and stationary contacts resulting in a burning and disintegration of these parts. Under these circumstances the entire switch is, for all practical purposes, rendered inoperative.

The above noted disadvantages of prior art constructions is overcome by the device of the instant invention by providing a switch head which utilizes a copper alloy spring and a specially shaped copper slug whose construction complements that of the spring so that upon closing of the switch the spring engages the stationary contacts before appreciable current begins to fiow. Thus, clamping action is assured so that there is adequate pressure between the stationary contacts and the slug and because of this, arcing will not take place from the stationary contacts to the spring. In addition, the fact that the spring is constructed of a good electrically conducting material aids the slug to carry high current for a sufficient time interval to allow a circuit breaker or fuse to open the faulted circuit.

Accordingly, a primary object of this invention is to provide a switch head capable of being closed on high fault currents without destroying the switch or rendering the switch inoperative for further use.

Another object is to provide a novel construction for a circuit interrupting device.

3,259,723 Patented July 5, 1966 Still another object is to provide a switch head having a novel contact slug.

A further object is to provide a switch head in which the contact slug and clamping spring complement one another so that the switch may be closed on a fault in a high current capacity circuit.

These as well as further objects of this invention shall become readily apparent after reading the following description of the accompanying drawings in which:

FIGURE 1 is an exploded perspective of a switch constructed in accordance with the teachings of the instant invention.

FIGURE 2 is a front elevation of the switch.

FIGURE 3 is a side elevation of the switch looking in the direction of arrows 3-3 of FIGURE 2.

FIGURE 4 is a cross-section of the switch.

FIGURES 5A through 5D are side elevations of the switch with the near side of the switch head housing removed so as to reveal the relative positions of the internal elements. In FIGURE 5A the switch is open; in FIG- URE 5B the contact slug is shown in initial engagement with the stationary contacts; in FIGURE 5C the spring is shown in initial engagement with the stationary contacts; and in FIGURE 5D the switch is fully closed.

Now referring to the figures. Switch 10 includes bacto-back L-shaped stationary terminal members 11, 12 whose rearwardly or upwardly extending legs 13, 14, respectively, constitute stationary contacts. Contacts 13, 14 are mounted in generally parallel relationship with the gap formed therebetween being provided for the passage of insulating barrier 15 and contact slug 16. Barrier 15 is integrally formed with molded switch head housing 17 while slug 16 is disposed within housing 17 to the rear of barrier 15 with the plane of barrier 15 in alignment with the plane of slug 16. Barrier 15 is disposed at the bottom or forward end of housing 17 with a portion of barrier 15 projecting forward of housing 17.

Barrier 15 lies parallel to walls 17a and 17b of housing 17 to form compartments within which stationary contacts 13, 14 are disposed. The rear portion of housing 17 is provided with internal guide slots 21a and 21b (FIGURE 1) whose forward ends are terminated by ledges 22a and 22b, respectively. Ends 23a and 2312 at the main section 23 of contact slug 16 are disposed within slots 21a and 21b, respectively, with slug surfaces 24a and 24b resting upon ledges 22a and 22b, respectively, to block downward movement of slug 16. The forward, or arcing edge, portion 25 of slug 16 is of reduced thickness for a reason which will hereinafter become obvious.

Also disposed within housing 17 is U-shaped clamping spring 30. Extensions 31a and 31b (FIGURE 1) of the spring web rest upon internal housing ledges 32a and 321), respectively, so as to limit forward movement of spring 30 and prevent tilting during assembly. Spring 30 is also positioned with the web thereof abutting the rear edge of contact slug 16 with the multifingered arms 30a and 30b of spring 30 being positioned opposite the faces of main section 23 of slug 16. Hollow spacer plug 35 is disposed within housing 17 to the rear of spring 30. Fibre insulator 36 closes off the rear end of housing 17 and is held in place by top plate 37 and U-shaped clamps 38 and 3-9.

The webs of clamps 38 and 39 lie in the undercuts at the forward ends of housing side projections 48, 49, respectively. The free ends of clamps 38 and 39 extend through clearance apertures in fibre sheet 36 and the cover portion 37a of top plate 37 with the free ends being peened over for securement purposes. Top plate 37 also includes a hook portion 37b which overlies cover portion 37a to form a space which receives bar 41 (FIG- With switch in the open position of FIGURE 5A,

arcing portion 25 of slug 16 is to the rear of stationary contacts 13, 14 and insulating barrier 15 extends partially to the rear of stationary contacts 13, 14. As the switch head moves forward, arcing portion passes between contacts 13, 14 without engaging either. Shortly thereafter main portion 23 of slug 16 engages stationary contacts 13, 14 at points A, B (FIGURE 5B). At this time copper alloy clamping spring is very close to but not in contact with the outer inclined surfaces of stationary contacts 13, 14 with the lower portions of spring arms 30a, 30b extending downwardly at least as far as the upper ends of contacts 13, 14.

For power source frequencies commonly encountered slug 16 and spring 30 will move from the positions shown in FIGURE 5B to those positions shown in FIGURE in no more than of a cycle. Since current flow through switch 10 does not commence until the elements thereto reach the position illustrated in FIGURE 5B, of a cycle thereafter the flow of current will not have increased to such a magnitude that magnetic forces generated thereby will be capable of separating stationary contacts 13, 14 from slug 16 nor will an arc strike to spring 30.

At the time of engagement of spring 30 with stationary contacts 13, 14 (FIGURE 5C), clamping action takes place so that pressure between contacts 13, 14 and slug 16 increases as bar 41 moves further downward. Spring 30, being constructed of good electrical contacting material, aids slug 16 to carry the high current for a sufficient time to permit a circuit breaker or fuse to open the faulted circuit. This action results in the protection of switch 10 and the device incorporating same.

Upon opening of switch 10, as clamping spring 30 disengages stationary contacts 13, 14 no arc will be formed since there is a low impedance path presented by slug 16. As soon as the main portion 23 of slug 16 separates from stationary contacts 13, 14 there is no longer any low impedance current path between the stationary contacts 13, 14 so that an arc passes to arcing portion 25 of slug 16 with this are being elongated as slug 16 moves upward. By the time switch 10 is in a fully open position (FIGURE 5D) the path between arcing portion 25 and stationary contacts 13, 14 is of relatively high impedance and the only direct air path between stationary contacts 13, 14 is elongated by the presence of that portion of insulating barrier 15 which extends to. the rear of stationary contacts 13, 14.

Thus, this invention provides a novel construction for a switch head with the construction being such that the contact slug and clamping spring complement one another to provide a switch which is capable of being closed on faulted high current circuits without destroying or rendering the switch inoperative for further use.

Although there has been described a. preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by the specific disclosure herein, but only by the appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are defined as follows:

1. An electric switch including a first and a' second stationary contact means having a first and a second contact section, respectively; said contact sections disposed in face to face relationship with a gap therebetween; a movable head including an insulating housing, a contact slug, an insulating barrier and a force applying device including biasing means; said slug and said device mounted to said housing and disposed therein; said contact sections extending rearwardly into said housing with said barrier positioned in said gap; said barrier positioned forwardly of said slug and being narrower than the Width of said gap when said switch is open; said slug including a main section and an arcing section disposed forward of said main section; said head guided by said contact sections for rectilinear movement between a first position wherein said switch is open and a second position wherein said switch is closed; said second position being forward of said first position; said slug positioned to the rear of said gap when said head is in said first position; said slug positioned within said gap when said switch is closed; said force applying device engaging outer surfaces of said contact sections when said switch is closed and urging confronting inner surfaces of said contact sections toward each other into good electrical contact with said main section; said force applying device being free of engagement with said outer surfaces when said head is in said first position; said arcing section being narrower than said main section and also being narrower than the width of said barrier; at the time of initial engagement between said contact sections and said slug as said head is moving from said first to said second position, said force applying device being free of engagement with said outer surfaces; said force applying device including a portion which, at said time of initial engagement, is positioned forward of the most rearwardly extending portions of said contact sections whereby upon closing of said switch said force applying means acts upon said contact sections before current through said switch can build up to a destructive value.

2. A switch as set forth in claim 1 in which the biasing means comprises a U-shaped spring element constructed of good electrically conducting material; said spring element positioned with its arms forwardly extending and engageable with said outer surfaces of said contact sections upon closing of said switch.

References Cited by the Examiner UNITED STATES PATENTS 2,287,676 6/1942 Frank et al. 200-146 X ROBERT K. SCHAEFER, Primary Examiner. ROBERT S. MACON, KATHLEEN H. CLAFFY,

Examiner's. P. E. CRAWFORD, Assistant Examiner. 

1. AN ELECTRIC SWITCH INCLUDING A FIRST AND A SECOND STATIONARY CONTACT MEANS HAVING A FIRST AND A SECOND CONTACT SECTION, RESPECTIVELY; SAID CONTACT SECTIONS DISPOSED IN FACE TO FACE RELATIONSHIP WITH A GAP THEREBETWEEN; A MOVABLE HEAD INCLUDING AN INSULATING HOUSING, A CONTACT SLUG, AN INSULATING BARRIER AND A FORCE APPLYING DEVICE INCLUDING BIASING MEANS; SAID SLUG AND SAID DEVICE MOUNTED TO SAID HOUSING AND DISPOSED THEREIN; SAID CONTACT SECTIONS EXTENDING REARWARDLY INTO SAID HOUSING WITH SAID BARRIER POSITIONED IN SAID GAP; SAID BARRIER POSITIONED FORWARDLY OF SAID SLUG AND BEING NARROWER THAN THE WIDTH OF SAID GAP WHEN SAID SWITCH IS OPEN; SAID SLUG INCLUDING A MAIN SECTION AND AN ARCING SECTION DISPOSED FORWARD OF SAID MAIN SECTION; SAID HEAD GUIDED BY SAID CONTACT SECTIONS FOR RECTILINEAR MOVEMENT BETWEEN A FIRST POSITION WHEREIN SAID SWITCH IS OPEN AND A SECOND POSITION WHEREIN SAID SWITCH IS CLOSED; SAID SECOND POSITION BEING FORWARD OF SAID FIRST PORTION; SAID SLUG POSITIONED TO THE REAR OF SAID GAP WHEN SAID HEAD IS IN SAID FIRST POSITION; SAID SLUG POSITIONED WITHIN SAID GAP WHEN SAID SWITCH IS CLOSED; SAID FORCE APPLYING DEVICE ENGAGING OUTER SURFACES OF SAID CONTACT SECTIONS WHEN SAID SWITCH IS CLOSED AND URGING CONFRONTING INNER SURFACES OF SAID CONTACT SECTIONS TOWARD EACH OTHER INTO GOOD ELECTRICAL CONTACT WITH SAID MAIN SECTION; SAID FORCE APPLYING DEVICE BEING FREE OF ENGAGEMENT WITH SAID OUTER SURFACES WHEN SAID HEAD IS IN SAID FIRST POSITION; SAID ARCING SECTION BEING NARROWER THAN SAID MAIN SECTION AND ALSO BEING NARROWER THAN THE WIDTH OF SAID BARRIER; AT THE TIME OF INITIAL ENGAGEMENT BETWEEN SAID CONTACT SECTIONS AND SAID SLUG AS SAID HEAD IS MOVING FROM SAID FIRST TO SAID SECOND POSITION, SAID FORCE APPLYING DEVICE BEING FREE OF ENGAGEMENT WITH SAID OUTER SURFACES; SAID FORCE APPLYING DEVICE INCLUDING A PORTION WHICH, AT SAID TIME OF INITIAL ENGAGEMENT, IS POSITIONED FORWARD OF THE MOST REARWARDLY EXTENDING PORTIONS OF SAID CONTACT SECTIONS WHEREBY UPON CLOSING OF SAID SWITCH SAID FORCE APPLYING MEANS ACTS UPON SAID CONTACT SECTIONS BEFORE CURRENT THROUGH SAID SWITCH CAN BUILD UP TO A DESTRUCTIVE VALUE. 